Wash lamb and remove any silver skin or excess fat or loose meat.
In a small bowl, mix mustard, rosemary, olive oil, lemon juice, garlic powder, fennel seed, onion powder, salt, and pepper. Spread liberally on the meaty side of lamb and brush on the bone side of the lamb avoiding contact with the rack bones.*
Cover lamb in plastic wrap and refrigerate for 4-24 hours.
Remove the lamb from the refrigerator and preheat oven to 450°F.
Place lamb on a foil-lined baking tray, meaty side up. Roast for 20 min or until internal temperature reaches 145°F (medium rare).
Remove from oven, place on cutting board, and tent with foil. Rest lamb for 10 minutes, then cut between the bones into chops (lollipops) and serve.
Notes
*Or carefully place marinade in a zip top bag, adding lamb without getting marinade on the bones. Refrigerate overnight.
Refrigerate leftovers for up to 4 days, or freeze for up to 3 months.